1. Field of the Invention
The invention generally relates to a method and device for cleaning vessels contaminated with dirt, such as slag or ashes, and, more particularly, toward a method and device for the on-line blast cleaning of combustion installations.
2. Description of Related Art
Heating surfaces in waste incineration plants and coal-fired boilers are subject to contamination with dirt. The dirt normally has inorganic compositions and is typically produced by deposits of ash particles on the walls. Areas in the zone of high flue gas temperatures are in most instances very hard because they remain stuck to the walls either in molten form, or melted on form, or else are stuck together on the wall by substances melting or condensing at lower temperatures, when these solidify on the colder boiler wall. Coatings of this kind can only be removed with difficulty and unsatisfactorily by known cleaning methods. This leads to the consequence that the boiler has to be switched off periodically, cooled down, and cleaned either manually or by means of sandblasting. Because boilers of this kind ordinarily have very large dimensions, it is frequently necessary to install scaffolding in the furnace for this purpose. This also requires an interruption of the operation lasting several days or weeks and apart from this, because of the substantial dust and dirt emissions it is exceedingly unpleasant and unhealthy for the cleaning personnel. A usually unavoidable accompanying phenomenon of the interrupted operation of an installation is damage to the vessel materials themselves as a consequence of the great temperature changes. Apart from the cleaning and repair costs, the stand-still costs or lost income from the installation due to the production represent an important overall cost factor.
Conventional cleaning methods, for example, are boiler beating and the utilisation of steam-jet cleaners, water-jet blowers/soot blowers and shot peening.
Known is a cleaning method in which the cooled down -and also the hot boiler still in operation is cleaned by means of the introduction and igniting of explosive devices. In the case of the method described in the document EP 1 067 349, a cooled explosive device by means of a cooled lance is brought into the proximity of the heating surface contaminated with dirt, where the explosive device is then ignited. The cakings on the heating surfaces are blasted off by force of the detonation, as well as by the vibrations of the wall produced by the shock waves. With this method, the cleaning time in comparison with the conventional cleaning methods is reduced significantly. With the necessary safety precautions, the cleaning can take place on-line, i.e., during the operation of the combustion furnace and while the vessel is still in a hot condition. With this method, the boiler may be cleaned in a matter of hours, while the conventional cleaning method would require days.
Disadvantageous in the case of the method described in EP 1 067 349 is the necessity of explosives. Apart from the high costs of the explosive material, in order to avoid accidents, for example, during the storage of the explosive material, elaborate security precautions have to be undertaken. The introduction of explosive material into a hot vessel in addition calls for an absolutely reliable and efficient cooling system, in order to prevent a premature detonation of the explosive material.